1. Field of the Invention
The present invention relates to a high-speed spinner for solid-state NMR measurements and, more particularly, to a high-speed spinner which is used for solid-state NMR measurements, provides a high rotational efficiency when a gas is blown at the spinner, and assures stable high-speed spinning.
2. Description of the Related Art
Interactions such as dipolar interactions are vanished in solutions by rotational Brownian motions. In NMR spectra of samples in solid state, such interactions manifest themselves directly. Therefore, the linewidths of the spectra are increased immensely. This conceals chemical shift terms. Consequently, in NMR spectra, signal peaks originating from various portions of a molecule under investigation cannot be separated. As a result, it has been considered that solid-state NMR spectroscopy is unsuited for analysis of molecular structures.
A method for overcoming this undesirable phenomenon and obtaining sharp solid-state NMR spectra was discovered by E. R. Andrew in 1958. In particular, a sample tube is tilted at a given angle to the direction of a static magnetic field and spun at a high speed. This removes anisotropic interactions and thus chemical shift terms can be extracted. This principle is known as MAS (magic-angle sample spinning).
To implement the magic-angle sample spinning, a solid sample placed in a static magnetic field must be spun at a high speed. However, it is not easy to obtain the required rotational speed of several kilohertz to tens of kHz. In the past, gas bearing technology has been adopted, and various methods have been proposed to obtain such rotational speeds.
FIG. 6 shows a conventional high-speed spinner for solid-state NMR spectroscopy. This spinner has a cylindrical stator 11 surrounding the outer surface of a rotor 12 with a slight space between them. The rotor 12 is sealed with a solid sample. A thrust rotor 14 is mounted at the lower end of the rotor 12 and placed opposite to a thrust stator 13 acting to cover the bottom of the cylindrical stator 11. The thrust rotor 14 acts to hold the position of the rotor 12 in the thrust direction. A turbine 16 is mounted at the top of the rotor 12 to apply a rotating force to the rotor 12 by means of jets of gas ejected from turbine nozzles 15 mounted in the stator 11. The rotor 12, thrust rotor 14, and turbine 16 together form a xe2x80x9crotor shaftxe2x80x9d rotating at a high speed.
FIG. 7 is a cross-sectional view taken on line b of FIG. 6 showing the conventional high-speed spinner for solid-state NMR measurements. As can be seen from FIG. 7, gas supply holes 20 are formed in the stator 11. A gas is continuously supplied into the stator 11 from the gas supply holes 20 to form a thin layer of gas in the space between the stator 11 and rotor 12. As a result, a journal gas bearing is formed. This creates a state of quite low frictional resistance between the stator 11 and rotor 12. The xe2x80x9crotor shaftxe2x80x9d can be spun at a high speed within the stator 11.
FIG. 8 is a cross-sectional view taken on line c of FIG. 6 showing the conventional high-speed spinner for solid-state NMR spectroscopy. As can be seen from FIG. 8, the plural turbine nozzles 15 are mounted eccentrically in the stator 11. Jets of gas ejected from the turbine nozzles 15 act on the blades of the turbine 16, applying a rotating force to the xe2x80x9crotor shaftxe2x80x9d. The jets of gas change their directions after acting on the turbine 16. The jets are expelled as gas streams 17 shown in FIG. 6 to the outside of the high-speed spinner.
Development of high-speed spinners using such a hydrostatic bearing was commenced by Doty et al. (U.S. Pat. No. 4,456,882). Then, Bartuska et al. have proposed a high-speed spinner comprising a combination of a hydrostatic bearing and a hydrodynamic bearing (U.S. Pat. No. 4,511,841). Doty et al. have attempted improvements of the hydrostatic bearing (U.S. Pat. No. 5,508,615).
The conventional high-speed spinners designed in this way and used for solid-state NMR measurements have some problems which have been great obstacles to increasing the rotational speeds of spinners.
The first problem is that large energy of gas jets is necessary to permit high-speed rotation of the spinner, because the resistance due to the viscosity of the gas on the journal bearing increases with increasing the rotational speed of the spinner but the efficiency of the force of the gas jets acting on the turbine decreases.
The second problem is associated with the hybrid type out of conventional, general NMR spinners (i.e., axial flow type, radial flow type, as well as the hybrid type). In the hybrid type, jets of gas are blown at a turbine from radial directions. The axial kinetic velocity varies when a force is acting on the turbine. This design is simple but the axial stability is low, because an axial force acts on the turbine. Especially, when the flow rate of the jets of gas is increased in an attempt to achieve higher-speed rotation, the thrust rotor and thrust stator will touch each other. This creates a great obstacle in increasing the spinning speed.
To overcome these two problems, Doty et al. (above-cited U.S. Pat. No. 5,508,615) adopted a radial in-flow turbine. However, this radial in-flow turbine has the disadvantage that the rigidity is reduced by the shape of the blades. The turbine of an NMR spinner is frequently damaged because the sample under measurement is often replaced. Hence, this design is disadvantageous in terms of practicality.
Another problem arises from the fact that the number of holes in the nozzles per circumference and the number of blades of the turbine have a common divisor. That is, the torque varies periodically in magnitude during one revolution of the turbine, making the rotation unstable.
In view of the foregoing, it is an object of the present invention to provide a high-speed spinner which is adapted for solid-state NMR measurements and which has a hybrid type turbine but provides a high efficiency of rotation when a gas is blown at the turbine, assures stable high-speed rotations, and permits the rotational speed to be monitored precisely.
A high-speed spinner adapted for solid-state NMR measurements and fabricated in accordance with the present invention comprises: a rotor portion capable of being sealed with a sample; and a stator portion surrounding the rotor portion. A gas is supplied into the space between the rotor and stator portions via gas supply holes to thereby form a gas bearing. The rotor portion is fitted with a turbine at which the gas is blown. This spinner is characterized in that the turbine vents the blown gas at a given angle to radial directions. In consequence, a rotating force is applied to the rotor portion itself.
The invention also provides a high-speed spinner for solid-state NMR measurements, the spinner comprising: a rotor portion capable of being sealed with a sample; and a stator portion surrounding the rotor portion. A gas is supplied into the space between the rotor and stator portions via gas supply holes to thereby form a gas bearing. The rotor portion is fitted with a turbine having blades. The gas is blown at the turbine. This spinner is characterized in that the number of the blades is greater than, and prime to, the number of the gas supply holes.
Furthermore, the invention provides a high-speed spinner for solid-state NMR measurements, the spinner comprising: a rotor portion capable of being sealed with a sample; and a stator portion surrounding the rotor portion. A gas is supplied into the space between the rotor and stator portions via gas supply holes to thereby form a gas bearing. The rotor portion is fitted with a turbine having blades, and the gas is blown at the turbine. This spinner is characterized in that the turbine vents the blown gas rearward at a given angle to radial directions. In consequence, a rotating force is applied to the rotor portion itself. The spinner is also characterized in that the number of the blades is greater than, and prime to, the number of the gas supply holes.
In another feature of the invention, the rotor has an auxiliary thrust stator extending in the thrust direction to carry the rotor portion while rotating it.
In a further feature of the invention, the given angle that the gas blown at the turbine forms with respect to radial directions when vented rearward is in the range of from 30xc2x0 to 60xc2x0.
In a still other feature of the invention, the diameter of the rotor portion is in the range of from 2 mm to 4 mm.
In a yet other feature of the invention, the length of the gas bearing is in the range of from 50% to 100% of the diameter of the rotor portion.
In an additional feature of the invention, the space between the rotor and stator portions is in the range of from 0.68% to 2.1% of the diameter of the rotor portion.
In a yet further feature of the invention, the space between the rotor and stator portions is in the range of from 27 xcexcm to 42 xcexcm.
In a still additional feature of the invention, the number of the gas supply holes for supplying the gas into the space between the rotor and stator portions is in the range of from 6 to 10.
In a still further feature of the invention, the diameter of each gas supply hole for supplying the gas into the space between the rotor and stator portions is in the range of from 0.2 mm to 0.4 mm.
In an additional feature of the invention, a thin metal film is formed on a part of the rotor portion to reflect light.
In an additional feature of the invention, the thin metal film is made of gold.
In an additional feature of the invention, the thickness of the thin metal film is in the range of from 10 nm to 1000 nm.
Other objects and features of the invention will appear in the course of the description thereof, which follows.